1. Field of the Invention
This invention relates in general to molding equipment and, more particularly, to an automatic continuously cycleable molding system which is ideally suited for encapsulation of electronic components and to a molding method therefor.
2. Description of the Prior Art
In molding equipment in general and in electronic component encapsulating equipment in particular, it has long been a practice to complete the entire molding cycle in a single, or at the most, two or three workstations. This type of prior art operation can be described as a batch operation in that one batch of parts is completed before another is started, or in some of the more sophisticated operations, there may be some overlapping of the various operations in successive batches.
In a typical prior art system for encapsulating integrated circuits, a plurality of such circuits are linearly arranged in a single workpiece, which is referred to as a leadframe. The premanufactured leadframes, which are to have the integrated circuits thereon encapsulated, are loaded into a bottom mold with the number of leadframes in a single batch being determined by mold size and the capacity of the particular molding equipment being used. The bottom mold is supported in the molding equipment, and after the leadframes are placed in the bottom mold, a top mold is moved into place atop the bottom mold. Some means is provided within the molding equipment to heat the molds to the proper temperature, and subsequently cool them for curing purposes. The heated molds are clamped together by the molding equipment and when the temperature is right, molding material, such as epoxy in pellet form, is placed in the mold set by being dropped into bores formed in the top mold of the mold set. Plungers are then inserted into the bores of the top mold on top of the epoxy pellets, and a pressurizing force is exerted on the plungers. The combination of the plunger force and the temperature causes the epoxy pellets to liquify and flow in the mold set to the cavities provided therein which determine the configuration and locations of the molded bodies which encapsulate the integrated circuits. Upon completion of this liquification and flow of the epoxy, the mold set is cooled to induce curing and subsequent thereto, the plungers are pulled from the mold set, the mold set is unclamped, and the top mold is lifted from the bottom mold. The leadframes are then removed from the bottom mold and carried to further equipment for degating, and otherwise operating on them to finish fabrication of the electronic circuit packages. The molds are then cleaned, if necessary, reheated and then they are ready for use in the next batch.
A rather substantial part of the above described typical prior art molding operation is accomplished by hand or under direct control of an operator or operators who determine timing and initiate the starting of the various operations. The need for operator participation is, of course, expensive, but the major problem is related directly to the limited production capability of such batch type operations. The need, for example, to continuously and repeatedly heat and cool the mold sets is very time consuming, and, of course, limits production.
Therefore, a need exists for a new and improved automatic continuously cycleable molding system which overcomes some of the problems and shortcomings of the prior art.